Dental materials curable by radical polymerization usually contain a polymerizable organic matrix and one or more fillers. In most cases, a mixture of monomers, initiators, stabilizers, pigments and further additives is used as polymerizable organic matrix (J. Viohl, K. Dermann, D. Quast, S. Venz, Die Chemie zahnärztlicher Füllungskunststoffe [The chemistry of dental filling plastics], Carl Hanser Verlag, Munich-Vienna 1986, 21-27). Such materials can be cured by thermal, redox-initiated or light-induced radical polymerization. Acidic monomers are also being used increasingly for the preparation of dental materials. These give the materials self-etching properties and improve their adhesion to the natural tooth substance.
Mixtures of dimethacrylates are usually used as resins (cf. A. Peutzfeldt, Resin composites in dentistry: the monomer systems, Eur. J. Oral Sci. 105 (1997) 97-116; J. W. Nicolson, H. M. Anstice, The chemistry of modern dental filling materials, J. Chem. Ed. 76 (1999) 1497-1501; J. W. Stansburry, Curing dental resins and composites by photopolymerization, J. Esthet. Dent. 12 (2000) 300-308; N. Moszner, T. Hirt, New Polymer-Chemical Developments in Clinical Dental Polymer Materials: Enamel-Dentin Adhesives and Restorative Composites, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 4369-4402).
In the case of adhesives, bisacrylamides are often used as cross-linker and acid group-containing methacrylates are mostly used as adhesive monomer (N. Moszner, U. Salz, J. Zimmermann, Chemical aspects of self-etching enamel-dentin adhesives: A systematic review, Dent. Mat. 21 (2005) 895-910). Examples of cross-linking dimethacrylates are 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)phenyl]propane (bis-GMA), 1,6-bis-[2-methacryloyloxyethoxycarbonylamino]-2,4,4-trimethylhexane (UDMA), decanediol-1,10-dimethacrylate, bismethacryloyloxy-methyltricyclo[5.2.1.]decane and triethylene glycol dimethacrylate (TEGDMA).
Acid monomers used commercially in dental materials are methacryloyloxydecyl dihydrogen phosphate (MDP), 2-methacryloyloxyethyl dihydrogen phosphate, 4-methacryloyloxyethyl trimellitic acid, 2-[4-dihydroxyphosphoryl)-2-oxabutyl]acrylic acid ethyl ester (EAEPA) and 2-acrylamido-2-methyl-1-propanesulphonic acid. It is known that acidic groups can etch and abrade the surface of the tooth structure, which leads to a mechanically improved substrate adhesion to the tooth structure. Moreover, acid groups can ionically bind the Ca2+ cations of the dentin/enamel surface, which also leads to an improved adhesion to the tooth structure.
In addition to acidic monomers, organic polymers with acidic groups are also regularly used for the preparation of dental materials. They are primarily used for the preparation of glass ionomer cements. These are dental cements which cure by means of an ionic reaction between the acidic groups of the polymer and an ion-releasing filler component. EP 0 323 120 B1 discloses glass ionomer cements which contain polymers which have, on the one hand, ionic groups for the ionic curing reaction and, on the other hand, light-curable groups. The ionic groups are carboxyl groups.
EP 0 796 607 B1 discloses the preparation of functionalized weakly acidic polycarboxylic acids by ring-opening metathesis polymerization (ROMP) of a monomer mixture of methacrylic acid-(5-norbornene-2-endo/exo-methyl)ester and bicyclo[2,2,1]hept-5-ene-2,3-endo/exo-dicarboxylic acid bis(tetrahydropyran-2-yl)ester followed by splitting off of the tetrahydropyran protective groups. The polycarboxylic acids are characterized by a high adhesion to various substrates and are suitable in particular for the preparation of glass ionomer cements.
EP 0 951 896 B1 and corresponding U.S. Pat. No. 6,281,271, which is hereby incorporated by reference, disclose dental materials which contain acidic oligomers which, in addition to methacrylate groups, have carboxyl groups. The materials cure, on the one hand, by means of an acid-base reaction between acidic oligomer and ion-releasing filler and, on the other hand, by means of radical polymerization.
EP 2 633 847 A2 and corresponding US 20160143818, which is hereby incorporated by reference, disclose glass ionomer cements which contain a weakly acidic copolymer of acrylic acid and itaconic acid anhydride that also has carboxyl groups.
U.S. Pat. No. 3,872,047, which is hereby incorporated by reference, discloses dental primers which contain a solution of a polymer with polar and non-polar groups in alcohol. The polar groups are said to bind to metal-containing surfaces. The non-polar groups are radically polymerizable and can react with a dental restoration material that is applied to a layer of the primer.